Multi-Carrier Transmission Device and Multi-Carrier Transmission Method

ABSTRACT

There is provided a multi-carrier transmission device capable of improving a packet error ratio in a system where transmission data is repeatedly multi-carrier-transmitted. In this device, the transmission data is subjected to error correction encoding in an error correction encoding unit ( 102 ), modulation in a modulation unit ( 104 ), and repetition in a repetition unit ( 106 ). A signal after the repetition (repetition bit) is two-dimensionally mapped in the frequency domain and the time domain according to a predetermined pattern in a mapping unit ( 108 ). The repetition bit transmission power is controlled so that the total value of the transmission power of repetition bit constituting one bit is identical to all the bits and the repetition bit of preferable reception quality has a large transmission power while the repetition bit of bad reception quality has a small transmission power.

TECHNICAL FIELD

The present invention relates to a multicarrier transmitting apparatusand multicarrier transmitting method.

BACKGROUND ART

When high-speed transmission is carried out in mobile communications,the effect of delayed waves due to multipath propagation cannot beignored, and transmission characteristics degrade due to frequencyselective fading. Therefore, multicarrier methods such as OFDM(Orthogonal Frequency Division Multiplexing) are now attractingattention as one kind of technology for combating frequency selectivefading. A multicarrier method is a technology that achieves high-speedtransmission by transmitting data using a plurality of carriers(subcarriers) whose transmission speed is suppressed to a level at whichfrequency selective fading does not occur. With the OFDM modulationmethod, in particular, the subcarriers on which data is placed aremutually orthogonal, making this the multicarrier modulation methodoffering the highest spectral efficiency. Moreover, the OFDM modulationmethod can be implemented with a comparatively simple hardwareconfiguration. For these reasons, OFDM is an object of particularattention, and various related studies are being undertaken.

As one example of such studies, a technology has been developed wherebyduplication (so-called “repetition”) of transmit data is performed, andtransmission is performed by OFDM (Non-patent Document 1).

A technology has also been developed whereby, in a multicarrier method,maximal-ratio combining type transmission power control is performedaccording to overall subcarrier quality information—that is, the lowerthe channel quality level of a subcarrier, the lower its transmissionpower is made, and the higher the channel quality level of a subcarrier,the higher its transmission power is made (Patent Document 1, PatentDocument 2). Hereinafter, for convenience, transmission by means of anOFDM method (or multicarrier method) will be referred to as “OFDM (ormulticarrier) transmission,” and transmission in which maximal-ratiocombining type transmission power control is performed will be referredto as “maximal-ratio combining transmission.”

Non-patent Document 1: Maeda, Atarashi, Kishiyama, Sawahashi,“Performance Comparisons between OFCDM and OFDM in a Forward LinkBroadband Channel”, Technical report of IEICE, RCS2002-162, August 2002

Patent Document 1: Japanese Patent Application Laid-Open No. 2000-358008

Patent Document 2: Japanese Patent Application Laid-Open No. HEI11-317723

DISCLOSURE OF INVENTION Problems to be Solved by the Invention

However, if the above two technologies are simply combined—that is, if atechnology whereby maximal-ratio combining transmission is performed forall subcarriers is applied to a system in which OFDM transmission isperformed using transmit data repetition—there is a risk of the power ofa particular bit being too low and unable to be received correctly,resulting in the occurrence of a packet error.

If, for example, transmission power is controlled low in all subcarriersto which a signal in which repetition of a particular bit is performedis assigned, that bit cannot be demodulated on the receiving side. As aresult, the packet containing that bit is regarded as an error packet,and the packet error rate deteriorates. An actual example will bedescribed later herein using a drawing.

It is an object of the present invention to provide a multicarriertransmitting apparatus and multicarrier transmitting method that enablethe packet error rate to be improved in a system in which multicarriertransmission is performed using transmit data repetition.

Means for Solving the Problems

A multicarrier transmitting apparatus of the present invention employs aconfiguration that includes: a duplication section that performsduplication (repetition) of transmit data; a mapping section that maps apost-duplication signal in the frequency domain and the time domain; atransmission power control section that performs transmission powercontrol of a post-mapping signal; and a transmitting section thattransmits a transmission-power-controlled signal using a multicarriermethod; wherein the transmission power control section performsmaximal-ratio combining type transmission power control within each bitor each symbol for the post-mapping signal while keeping thetransmission power assigned to each bit or each symbol constant.

ADVANTAGEOUS EFFECT OF THE INVENTION

The present invention enables the packet error rate to be improved in asystem in which multicarrier transmission is performed using transmitdata repetition.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a drawing showing repetition bit transmission power whenconventional technologies are simply combined;

FIG. 2 is a drawing showing repetition bit received power whenconventional technologies are simply combined;

FIG. 3 is a block diagram showing the configuration of a multicarriertransmitting apparatus according to one embodiment of the presentinvention;

FIG. 4 is a drawing explaining the operation of a multicarriertransmitting apparatus according to this embodiment;

FIG. 5 is a drawing showing another example of a mapping method;

FIG. 6 is a drawing showing yet another example of a mapping method;

FIG. 7A is a drawing showing the reception quality of each subcarrier ata certain time;

FIG. 7B is a drawing showing the reception quality of each subcarrier atanother time;

FIG. 8A is a drawing showing the reception quality of each repetitionbit at a certain time;

FIG. 8B is a drawing showing the reception quality of each repetitionbit at another time;

FIG. 9 is a drawing showing the transmission power of repetition bitsaccording to this embodiment; and

FIG. 10 is a drawing showing the received power of repetition bitsaccording to this embodiment.

BEST MODE FOR CARRYING OUT THE INVENTION

An embodiment of the present invention will now be described in detailwith reference to the accompanying drawings.

FIG. 3 is a block diagram showing the configuration of a multicarriertransmitting apparatus according to one embodiment of the presentinvention.

Multicarrier transmitting apparatus (hereinafter referred to simply as“transmitter”) 100 shown in FIG. 3 is a system that performs OFDMtransmission using repetition of transmit data (hereinafter referred toas “repetition OFDM”), and has an error correction coding section 102, amodulation section 104, a repetition section 106, a mapping section 108,a transmission power control section 110, an OFDM transmitting section112, a transmit RF (Radio Frequency) section 114, a dual-functiontransmitting/receiving antenna 116, a receive RF section 118, a channelquality information extraction section 120, a transmission power valuecalculation section 122, a transmission power distribution calculationsection 124, and a transmission power calculation section 126.Transmitter 100 is installed, for example, in a base station apparatusin a multicarrier (in this embodiment, OFDM) mobile communicationsystem.

Error correction coding section 102 performs error correction coding ata predetermined coding rate, such as R=1/2, for example, on transmitdata output from a baseband section or the like (not shown), and outputstransmit data after error correction coding to modulation section 104.

Modulation section 104 generates a transmit symbol by modulatingtransmit data output from error correction coding section 102 using apredetermined modulation method. The generated symbol is output torepetition section 106.

Repetition section 106 duplicates a transmit symbol output frommodulation section 104 until a predetermined number of duplicates arereached, and outputs the duplicated transmit symbols to mapping section108. A signal output from repetition section 106—that is, apost-repetition signal—will hereinafter be referred to as a “repetitionbit.”

Mapping section 108 maps repetition bits output from repetition section106 in accordance with a predetermined mapping method. For example,repetition bits are mapped 2-dimensionally in the frequency domain andtime domain based on a predetermined pattern. At this time, repetitionbits are mapped while being interleaved in the frequency domain and/ortime domain. Post-mapping transmit data (repetition bits) are output totransmission power control section 110. Mapping section 108 outputsmapping processing results to transmission power distributioncalculation section 124. An actual example of a mapping method will bedescribed later herein.

Transmission power control section 110 controls repetition bittransmission power in accordance with calculation results oftransmission power calculation section 126. Transmission power controlwill be described in detail later herein.

OFDM transmitting section 112 generates an OFDM signal that hasundergone repetition processing by performing OFDM transmissionprocessing on a transmission-power-controlled signal. Specifically, forexample, a transmission-power-controlled signal undergoes Inverse FastFourier Transform (IFFT) processing, then the IFFT-processed parallelsignal undergoes parallel/serial conversion to a serial signal, and aGuard Interval (GI) is inserted in the obtained serial signal (OFDMsignal). After GI insertion, the OFDM signal is output to transmit RFsection 114.

Transmit RF section 114 has a digital/analog converter, low-noiseamplifier, bandpass filter, and so forth, and executes predeterminedradio processing such as up-conversion on the OFDM signal output fromOFDM transmitting section 112. After radio processing, the OFDM signalis transmitted as a radio signal from antenna 116.

A radio signal transmitted from antenna 116 is received by acommunication terminal apparatus such as a mobile station apparatus in amobile communication system. The communication terminal apparatusmeasures the reception quality of a signal transmitted from transmitter100 on a subcarrier-by-subcarrier basis, and transmits the receptionquality of each subcarrier to transmitter 100 as channel qualityinformation. At this time, channel quality information is transmittedcontained in a signal transmitted from the communication terminalapparatus to transmitter 100, for example.

Receive RF section 118 has an analog/digital converter, low-noiseamplifier, bandpass filter, and so forth, and executes predeterminedradio processing such as down-conversion on a signal received by antenna116. An output signal (baseband signal) from receive RF section 118 isoutput to channel quality information extraction section 120.

Channel quality information extraction section 120 extracts channelquality information (per-subcarrier reception quality) from the receiveRF section 118 output signal (baseband signal). The extracted channelquality information is output to transmission power distributioncalculation section 124.

Transmission power value calculation section 122 calculates a per-symboltransmission power value. Specifically, for example, transmission powervalue calculation section 122 receives information on the number oftransmit symbols and information on total transmission power from anupper layer in which radio resource allocation is performed, and usesthese two items of information (transmit symbol number information andtotal transmission power information) to calculate a per-symboltransmission power value (transmission power value per symbol=totaltransmission power÷number of transmit symbols). The calculatedper-symbol transmission power value is output to transmission powerdistribution calculation section 124.

Transmission power distribution calculation section 124 calculates thetransmission power distribution within one symbol using the mappingprocessing results output from mapping section 108, channel qualityinformation (per-subcarrier reception quality) output from channelquality information extraction section 120, and the per-symboltransmission power value output from transmission power valuecalculation section 122. Specifically, for example, transmission powerdistribution calculation section 124 checks the reception quality ofeach repetition bit based on the reception quality of each subcarrierreported from the receiving side (communication terminal apparatus), andcalculates transmission power distribution within one symbol so that thetotal value of transmission power of repetition bits composing one bitis the same for all bits, and so that transmission power is greater fora repetition bit with good reception quality and smaller for arepetition bit with poor reception quality. The calculated transmissionpower distribution within one symbol is output to transmission powercalculation section 126.

Transmission power calculation section 126 calculates the transmissionpower value of each repetition bit in one symbol in accordance with thetransmission power distribution within one symbol output fromtransmission power distribution calculation section 124. The calculationresults are output to transmission power control section 110.

Next, the principal operations of transmitter 100 having the aboveconfiguration will be described using FIG. 4 through FIG. 10.

FIG. 4(A) shows transmit data before error correction coding, FIG. 4(B)shows transmit data after error correction coding, FIG. 4(C) shows asignal after repetition (repetition bits), and FIG. 4(D) shows theresult of repetition bit mapping. FIG. 5 is a drawing showing anotherexample of a mapping method, and FIG. 6 is a drawing showing yet anotherexample of a mapping method. FIG. 7A is a drawing showing the receptionquality of each subcarrier at a certain time, and FIG. 7B is a drawingshowing the reception quality of each subcarrier at another time. FIG.8A is a drawing showing the reception quality of each repetition bit ata certain time, and FIG. 8B is a drawing showing the reception qualityof each repetition bit at another time. FIG. 9 is a drawing showing thetransmission power of repetition bits according to this embodiment, andFIG. 10 is a drawing showing the received power of repetition bitsaccording to this embodiment. FIG. 1 is a drawing for comparison withFIG. 9, showing repetition bit transmission power when conventionaltechnologies are simply combined, and FIG. 2 is a drawing for comparisonwith FIG. 10, showing repetition bit received power when conventionaltechnologies are simply combined.

Transmitter 100 first performs error correction coding of transmit datausing a predetermined coding rate in error correction coding section102. For example, the transmit data shown in FIG. 4(B) is obtained byperforming error correction coding of the transmit data shown in FIG.4(A) with coding rate R=1/2. For the sake of simplicity, FIG. 4(A) showsonly 2 bits.

Then, in modulation section 104, a transmit symbol is generated bymodulating transmit data output from error correction coding section 102(see FIG. 4(B)) using a predetermined modulation method. There are noparticular restrictions on the modulation method used by modulationsection 104, and any modulation method can be used, including BPSK(Binary Phase Shift Keying), QPSK (Quadrature Phase Shift Keying), 16QAM(Quadrature Amplitude Modulation), 64QAM, 256QAM, and so forth.

Repetition section 106 then duplicates the transmit symbol output frommodulation section 104 until a predetermined number of duplicates arereached. For example, each bit of the 4-bit signal shown in FIG. 4(B) isduplicated three times, giving the 16-bit signal (repetition bits) shownin FIG. 4(C). Here, a1, a2, a3, and a4 are a and its duplicates, b1, b2,b3, and b4 are b and its duplicates, c1, c2, c3, and c4 are c and itsduplicates, and d1, d2, d3, and d4 are d and its duplicates. Next,mapping section 108 maps the repetition bits output from repetitionsection 106 (see FIG. 4(C)) in accordance with a predetermined mappingmethod. For example, repetition bits are mapped 2-dimensionally in thefrequency domain and time domain as shown in FIG. 4(D) based on apredetermined pattern. Here, repetition bits are mapped while beinginterleaved in the frequency domain and time domain.

When the above-described 2-dimensional mapping is performed by mappingsection 108, it is desirable for a following mapping method to be used.Firstly, signals that have undergone repetition are not arranged inadjacent positions, as shown in FIG. 5 for example, and secondly,signals 130 that have undergone repetition are arranged so as to bemutually separated when mapped, as shown in FIG. 6, for example, andsignals of another channel are transmitted in the part 132 between theseparated signals 130.

Through use in combination with repetition OFDM, the mapping methodshown in FIG. 5 or FIG. 6 offers improved performance, throughattainment of the following effect, compared with use in combinationwith an OFDM method that includes spreading—that is, a method combiningCDMA (Code Division Multiple Access) and OFDM (called both MC(multicarrier)-CDMA and OFDM-CDMA).

With an OFDM method that includes spreading, performance degrades ifpost-spreading signals (chip data) are arranged in separated positions.The reason for this is as follows. When signals are code-multiplexed inCDMA, if the variance of post-spreading signal received power is large,inter-code interference occurs and reception SIR degrades, leading to amajor degradation of reception error rate characteristics. In thisregard, when chip data are arranged in separated positions in an OFDMmethod that includes spreading, the variance of post-spreading signal(chip data) received power becomes large. This is because, when signalsare arranged in separated positions, propagation path differencesbetween places at which chip data are arranged are great due to theeffects of frequency selective fading, and differences in received poweralso become great. Therefore, if chip data are arranged in separatedpositions in an OFDM method that includes spreading, inter-codeinterference occurs and reception SIR degrades, and reception error ratecharacteristics deteriorate significantly.

In contrast, the kind of performance degradation described above doesnot occur with repetition OFDM. The reason for this is as follows. Sincesignals are not code-multiplexed in repetition OFDM, inter-codeinterference does not occur even if the variance of post-repetitionsignal received power is large. Therefore, SIR degradation does notoccur and reception error rate characteristics do not deteriorate. Onthe contrary, with repetition OFDM, performance actually improves as thevariance of post-repetition signal received power increases. This isbecause diversity gain can be obtained on the receiving side by means ofmaximal-ratio combining in post-repetition signal reception.

Transmission power control section 110 then controls repetition bittransmission power in accordance with the processing results oftransmission power value calculation section 122, transmission powerdistribution calculation section 124, and transmission power calculationsection 126. Specifically, transmission power value calculation section122 first receives information on the number of transmit symbols andinformation on total transmission power from an upper layer, and usesthese two items of information (transmit symbol number information andtotal transmission power information) to calculate a per-symboltransmission power value (transmission power value per symbol=totaltransmission power÷number of transmit symbols). Transmission powerdistribution calculation section 124 then checks the reception qualityof each repetition bit (see FIG. 8A and FIG. 8B) based on the result ofmapping processing output from mapping section 108 (see FIG. 4(D)) andthe reception quality of each subcarrier reported from the receivingside (see FIG. 7A and FIG. 7B), and calculates transmission powerdistribution within one symbol so that the total value of transmissionpower of repetition bits composing one bit is the same for all bits, andso that transmission power is greater for a repetition bit with goodreception quality and smaller for a repetition bit with poor receptionquality (see FIG. 9). Then transmission power calculation section 126calculates the transmission power value of each repetition bit in onesymbol in accordance with that transmission power distribution withinone symbol.

For the mapping results shown in FIG. 4(D), for example, if thereception quality of each subcarrier at respective times is assumed tobe as shown in FIG. 7A and FIG. 7B, the reception quality of eachrepetition bit is determined to be as shown in FIG. 8A and FIG. 8Brespectively.

At this time, in this embodiment, control is performed so that the totalvalue of transmission power of repetition bits composing a particularbit is the same for all bits. Specifically, control is performed so thata1+a2+a3+a4=b1+b2+b3+b4=c1+c2+c3+c4=d1+d2+d3+d4. That is to say,transmission power is controlled so as to be a fixed value from a bitunit standpoint.

For example, if the number of transmit symbols is 4 and the totaltransmission power is 80, first, distributing the total transmissionpower (80) equally among the transmit symbols gives a per-symboltransmission power value of 20. Then the per-symbol transmission powervalue (20) is further distributed according to the channel quality(reception quality) ratio within each transmit symbol. From FIG. 8A andFIG. 8B, it can be seen that the reception quality ratio of a1, a2, a3,and a4 is 8:8:4:4, the reception quality ratio of b1, b2, b3, and b4 is2:2:1:1, the reception quality ratio of c1, c2, c3, and c4 is 6:8:6:8,and the reception quality ratio of d1, d2, d3, and d4 is 3:8:3:8.Therefore, distributing the per-symbol transmission power value withineach transmit symbol (20) according to the reception quality ratiosgives transmission power values, as shown in FIG. 9, of 6.6, 6.6, 3.4,and 3.4 respectively for a1, a2, a3, and a4; 6.6, 6.6, 3.4, and 3.4respectively for b1, b2, b3, and b4; 4.3, 5.7, 4.3, and 5.7 respectivelyfor c1, c2, c3, and c4; and 2.7, 7.3, 2.7, and 7.3 respectively for d1,d2, d3, and d4. That is to say, in this embodiment, maximal-ratiocombining transmission is performed in each bit so that the transmissionpower assigned to each bit is the same. At this time, the square oftransmission power appears in a received signal due to fading, andtherefore the received power of each repetition bit is as shown in FIG.10. That is to say, reception quality is satisfactory for all bits,enabling all bits to be received correctly.

Thus, in this embodiment, since transmission power is controlled so asto be a fixed value from a bit unit standpoint, the transmission powerof a specific bit does not fall to an extreme degree. This enables thepacket error rate to be improved.

In contrast, when a technology whereby maximal-ratio combiningtransmission is performed for subcarriers overall is simply applied to asystem in which OFDM transmission is performed using transmit datarepetition, maximal-ratio combining type transmission power control isperformed according to the overall subcarrier reception quality, so thatthere is a risk that the transmission power of a particular bit will betoo low to be received correctly, as described above, and a packet errorwill occur.

For example, when the reception quality of each repetition bit is asshown in FIG. 8A and FIG. 8B, if the total transmission power (80)equally is distributed according to the channel quality (receptionquality) ratios, the transmission power values of a1, a2, a3, a4, b1,b2, b3, b4, c1, c2, c3, c4, d1, d2, d3, and d4 are, respectively, 8, 8,4, 4, 2, 2, 1, 1, 6, 8, 6, 8, 3, 8, 3, and 8. At this time, the squareof transmission power appears in a received signal due to fading, andtherefore the received power of each repetition bit is as shown in FIG.2.

That is to say, as the subcarriers of repetition bits b1 through b4composing bit “b” have low reception quality (see FIG. 8A and FIG. 8B),they are transmitted at low power (see FIG. 1). Therefore, on thereceiving side, the received power of repetition bits b1 through b4 isexcessively low (the area indicated by reference code 140 in FIG. 2) andcannot be received correctly, and bit “b” cannot be demodulatedcorrectly. If bit “b” is incorrectly demodulated, the packet containingthat bit is processed as an error packet, and thus the entire packet isprocessed as an erroneous packet and system throughput fallssignificantly.

Thus, according to this embodiment, maximal-ratio combining typetransmission power control is performed within each bit while keepingthe transmission power assigned to each bit constant, thereby making itpossible to avoid a situation in which subcarriers with low transmissionpower are concentrated in a specific bit, and enabling the packet errorrate to be improved.

In the above embodiment, a case has been described by way of example inwhich the present invention is configured as hardware, but it is alsopossible for the present invention to be implemented by software.

The function blocks used in the description of the above embodiment aretypically implemented as LSIs, which are integrated circuits. These maybe implemented individually as single chips, or a single chip mayincorporate some or all of them. Here, the term LSI has been used, butthe terms IC, system LSI, super LSI, and ultra LSI may also be usedaccording to differences in the degree of integration.

The method of implementing integrated circuitry is not limited to LSI,and implementation by means of dedicated circuitry or a general-purposeprocessor may also be used. An FPGA (Field Programmable Gate Array) forwhich programming is possible after LSI fabrication, or a reconfigurableprocessor allowing reconfiguration of circuit cell connections andsettings within an LSI, may also be used.

In the event of the introduction of an integrated circuit implementationtechnology whereby LSI is replaced by a different technology as anadvance in, or derivation from, semiconductor technology, integration ofthe function blocks may of course be performed using that technology.The adaptation of biotechnology or the like is also a possibility.

The present application is based on Japanese Patent Application No.2004-199380 filed on Jul. 6, 2004, entire content of which is expresslyincorporated herein by reference.

INDUSTRIAL APPLICABILITY

A multicarrier transmitting apparatus and multicarrier transmittingmethod of the present invention have an effect of enabling the packeterror rate to be improved in a system in which multicarrier transmissionis performed using transmit data repetition, and are suitable for use ina base station apparatus or the like in a multicarrier mobilecommunication system.

1. A multicarrier transmitting apparatus comprising: a duplicationsection that duplicates transmit data; a mapping section that maps apost-duplication signal in a frequency domain and a time domain; atransmission power control section that performs transmission powercontrol of a post-mapping signal; and a transmitting section thattransmits a transmission-power-controlled signal using a multicarriermethod, wherein the transmission power control section performsmaximal-ratio combining type transmission power control within each bitor each symbol for the post-mapping signal while keeping transmissionpower assigned to each bit or each symbol constant.
 2. The multicarriertransmitting apparatus according to claim 1, further comprising anacquisition section that acquires per-subcarrier channel qualityinformation; wherein the transmission power control section has: a firstcalculation section that calculates per-bit or per-symbol transmissionpower based on transmit bit number information and total transmissionpower information; and a second calculation section that, based onobtained per-subcarrier channel quality information and calculatedper-bit or per-symbol transmission power, calculates transmission powerwithin each bit or each symbol so that, as a result of the mapping,transmission power assigned to each bit or each symbol is the same forall bits or all symbols, and so that transmission power is greater for asignal assigned to a subcarrier with good channel quality andtransmission power is smaller for a signal assigned to a subcarrier withpoor channel quality among signals composing each bit or each symbol. 3.The multicarrier transmitting apparatus according to claim 1, whereinthe mapping section performs mapping while interleaving post-duplicationsignals in a frequency domain and/or time domain.
 4. The multicarriertransmitting apparatus according to claim 1, wherein the mapping sectionperforms mapping so that post-duplication signals are not arranged inadjacent positions.
 5. The multicarrier transmitting apparatus accordingto claim 1, wherein the mapping section arranges post-duplicationsignals so as to be mutually separated when mapped and arranges a signalof another channel between the separated post-duplication signals.
 6. Amulticarrier transmitting method comprising: a duplication step ofduplicating transmit data; a mapping step of mapping a post-duplicationsignal in a frequency domain and a time domain; a transmission powercontrol step of performing transmission power control of a post-mappingsignal; and a transmitting step of transmitting atransmission-power-controlled signal using a multicarrier method,wherein, in the transmission power control step, maximal-ratio combiningtype transmission power control is performed within each bit or eachsymbol for the post-mapping signal while keeping transmission powerassigned to each bit or each symbol constant.